This disclosure relates to exits for headphone ports. U.S. Pat. No. 7,916,888 describes an in-ear headphone design in which two acoustic ports, one acoustically reactive and one acoustically resistive, are provided to couple the cavity enclosing the back side of an electroacoustic transducer to the environment, as shown in FIG. 7. That patent described a particular method of constructing the headphone, as shown in FIG. 8. In that design, a first region 12 of the earphone 10 includes a rear chamber 14 and a front chamber 16 defined by shells 15 and 17, respectively, on either side of an electroacoustic transducer, or driver, 18. The front chamber 16 extends through a second region 20 to the entrance to the ear canal, and in some embodiments into the ear canal, through a cushion 22 and ends at an acoustic resistance element 24. An acoustic resistance element is something that dissipates a proportion of acoustic energy that impinges on or passes through it. The rear chamber 14 is sealed around the back side of the driver 18 by the shell 15. The rear chamber 14 is acoustically coupled to the environment through a reactive element, such as a reactive port (also referred to as a mass port) 26, and a resistive element, which may also be formed as a resistive port 28. U.S. Pat. No. 6,831,984 describes the use of parallel reactive and resistive ports in a headphone device, and is incorporated here by reference. Although we refer to acoustic ports as reactive or resistive, in practice any acoustic port will have both reactive and resistive effects. The term used to describe a given acoustic port indicates which effect is dominant.
A reactive port like the port 26 is, for example, a tube-shaped opening in what may otherwise be a sealed acoustic chamber, in this case rear chamber 14. In the example of FIG. 8, the reactive port 26 is defined by voids in an inner spacer 30, the shell 15, and an outer cover 32. When these three parts are assembled together, the voids in them are combined to form a tube connecting the volume enclosed by the rear chamber 14 to the environment through an opening 34 in the side of the shell 15. A resistive port like the port 28 is, for example, a small opening in the wall of an acoustic chamber covered by a material providing an acoustical resistance, for example, a wire or fabric screen, that allows some air and acoustic energy to pass through the wall of the chamber. In the example of FIG. 8, the resistive port 28 formed by covering a hole in the spacer 30 with a resistive screen, and providing a path through the shell, to the environment, that does not provide any additional acoustic impedance.